Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$35.76	12.810%	$40.3409	$40.34	$40.35	$40.30
Purchase #2	$119.75	11.275%	$133.2518	$133.25	$133.25	$133.30
Purchase #3	$84.66	4.680%	$88.6221	$88.62	$88.60	$88.60
Purchase #4	$41.60	8.428%	$45.106	$45.11	$45.10	$45.10
Purchase #5	$164.35	12.493%	$184.8822	$184.88	$184.90	$184.90
Purchase #6	$137.86	13.589%	$156.5938	$156.59	$156.60	$156.60
Purchase #7	$141.63	3.820%	$147.0403	$147.04	$147.05	$147.00
7 purchase totals =	$725.61		$795.8371	$795.83	$795.85	$795.80